<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>方块跳动加载</title>
    <style>
        body {
            height: 100vh;
            display: flex;
            justify-content: center;
            align-items: center;
            background-color: black;
        }

        div {
            display: flex;
            flex-flow: row nowrap;
            align-items: center;
            justify-content: space-between;
            width: 2em;
        }

        span {
            display: block;
            width: 0.3em;
            height: 1em;
            background-color: #3cefff;
        }

        span:nth-of-type(1) {
            animation: grow 1s -0.45s ease-in-out infinite;
        }

        span:nth-of-type(2) {
            animation: grow 1s -0.3s ease-in-out infinite;
        }

        span:nth-of-type(3) {
            animation: grow 1s -0.15s ease-in-out infinite;
        }

        span:nth-of-type(4) {
            animation: grow 1s ease-in-out infinite;
        }

        @keyframes grow {
            0%,
            100% {
                transform: scaleY(1);
            }
            50% {
                transform: scaleY(2);
            }
        }
    </style>
</head>
<body>
<div>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
</div>
</body>
</html>